Working Principle Of Voltage Transformer

Its working principle is the same as that of a transformer, and its basic structure is also an iron core and primary and secondary windings. The characteristic is that the capacity is very small and relatively constant, and it is close to the no-load state during normal operation.
The impedance of the voltage transformer itself is very small, and once a short circuit occurs on the secondary side, the current will rapidly increase and burn out the coil. For this reason, the primary side of the voltage transformer is connected to a fuse, and the secondary side is reliably grounded to avoid high potential to the ground on the secondary side that may cause personal and equipment accidents when the insulation of the primary and secondary sides is damaged.
Voltage transformers for measurement are generally made into single-phase double coil structures, with the primary voltage being the measured voltage (such as the line voltage of the power system). They can be used in single-phase or two connected in V-V shape for three-phase use. Voltage transformers used in laboratories often have multiple taps on the primary side to meet the needs of measuring different voltages. The voltage transformer for protective grounding also comes with a third coil, called a three coil voltage transformer. The third coil of the three-phase is connected into an open triangle, and the two outgoing terminals of the open triangle are connected to the voltage coil of the grounding protection relay.
During normal operation, the three-phase voltage of the power system is symmetrical, and the sum of the three-phase induced electromotive forces on the third coil is zero. Once single-phase grounding occurs, the neutral point will shift, and zero sequence voltage will appear between the terminals of the open triangle, causing the relay to act, thus providing protection for the power system.
If zero sequence voltage occurs in the coil, zero sequence magnetic flux will appear in the corresponding iron core. Therefore, this three-phase voltage transformer adopts a side yoke type iron core (for 10kV and below) or three single-phase voltage transformers. For this type of transformer, the accuracy requirement of the third coil is not high, but it requires certain overexcitation characteristics (that is, when the primary voltage increases, the magnetic flux density in the iron core also increases by a corresponding multiple without damage).
Voltage transformer is an indispensable electrical appliance in transmission and power supply systems such as power plants and substations. Precision voltage transformer is an instrument used in electrical testing laboratories to expand the measurement limit and measure voltage, power, and electrical energy. Voltage transformers and transformers are very similar in that they are used to change the voltage on the line.
Why does it need to change voltage on the circuit? This is because the voltage on the line varies greatly depending on the different conditions of power generation, transmission, and consumption. Some are low voltage 220V and 380V, while others are high voltage tens of thousands or even hundreds of thousands of volts. To directly measure these low and high voltage voltages, it is necessary to create corresponding low and high voltage voltmeters and other instruments and relays based on the size of the line voltage. This not only brings great difficulties to the production of instruments, but more importantly, it is impossible and absolutely not allowed to directly produce high-voltage instruments and measure voltage directly on high-voltage lines.